The present invention relates to a propeller construction of an electric fan, and particularly to a propeller construction of an electric fan wherein each rotatable blade is provided at the outer end thereof with an arcuate rib for preventing the back-flow of fluid so that the velocity and quantity of fluid flowing out of the propeller can be increased.
In a conventional propeller construction of an electric fan, each rotatable blade extends smoothly from a center support portion thereof to form a certain involute angle. As such propeller rotates, a differential pressure is generated between the front and the back of each rotatable blade, that is, the front and the back of the outer end of each blade. This differential pressure results in the back-flow of fluid, so that the velocity and quantity of fluid effected at the front fluid-blowing side of the propeller may be reduced.
FIG. 6(a) is a plot explaining the pressure distribution at the front and back sides of the conventional propeller and the static pressure curve thereof. As apparent from FIG. 6(a), the pressure P.sub.1 at the upstream side with respect to the motive zone A of the propeller 1, that is, at the fluid-sucking side B is reduced by the pressure P.sub.2 at the just-back of the propeller 1, as the streamline of fluid proceeds in the axial direction indicated by an arrow.
As a result of the increase of the momentum of the propeller 1 due to the rotating force thereof, however, the pressure of fluid is severely increased by the pressure P.sub.3 at the just-front of the propeller 1, as compared with the pressure P.sub.2 at the just-back of the propeller 1. Thereafter, the pressure of the fluid is gradually, decreased by the pressure P.sub.4 at the downstream side, that is, the fluid-blowing side C of the propeller.
Thus, the pressure of the fluid passing through the propeller 1 is discontinuous, in that a differential pressure is generated between the just-front and just-back sides of the propeller 1. Thereby, a back-flow is generated near the outer end of each blade, so that the quantity of the blown fluid is decreased.